1. Field of the Invention
The invention relates to a fuel rod for a nuclear reactor, having a metal cladding tube being filled with nuclear fuel, a metal seal plug, locking plug or stopper being welded to one end of the tube and in particular being formed of the same metal, and an annular bead on the outer surface of the cladding tube at a transition point between the cladding tube and the seal plug. The invention also relates to a welding apparatus for producing the fuel rod.
Such a fuel rod is already typical and its annular bead has a sharp annular gradient. In other words, the cross section of the annular bead forms an acute triangle with an acute angle located at the annular gradient. Such a fuel rod can be produced in a welding apparatus with an electrode in which there is a bore for receiving one end of a cladding tube. The bore is chamfered, forming a frustoconical void that tapers toward the inside, on an end of the bore that faces toward a counter electrode which is displaceable relative to the aforementioned electrode and is intended to hold the seal plug. The frustoconical void determines the shape of the annular bead that forms from solidified welding melt when the seal plug is permanently welded to the cladding tube.
The welded connection between the cladding tube and the seal plug is considered perfect if the frustoconical void of the electrode for the cladding tube is filled to a predetermined extent during welding with material of the cladding tube and the seal plug, which is ascertainable by experimentation. After the welding, the quality of the weld can be determined by measuring the height of the gradient of the annular bead at the weld between the seal plug and the cladding tube of the fuel rod.
In order to produce nuclear reactor fuel assemblies that can be inserted into a nuclear reactor, the fuel rods must be threaded into a mesh of spacers, which as a rule are lattice-like. The annular bead at the weld between the cladding tube and the seal plug of the individual fuel rods is a hindrance to the threading operation. Therefore, after the quality of the weld has been measured and ascertained, the annular beads are mechanically machined down, for instance by being milled off, until it can be assumed that they will no longer hinder the threading of the fuel rods into the spacers.
In the mechanical machining down process, damage to the cladding tube can occur, causing a fuel rod to be rejected.